136 Evolution and Adaptation 
variations, which sooner or later became constant through the 
nature of the organism and of the surrounding conditions, as 
well as through the intercrossing of distinct individuals, but 
not through natural selection; for as these morphological 
characters do not affect the welfare of the species, any slight 
deviations in them could not have been governed or accumu- 
lated through this latter agency. It is a strange result which 
we thus arrive at, namely, that characters of slight vital im- 
portance to the species are the most important to the system- 
atist; but, as we shall hereafter see when we treat of the 
genetic principle of classification, this is by no means so para- 
doxical as it may at first appear.” ; 
If all this be granted, it is once more evident that the only 
variations that come under the action of selection are the 
limited number that are of vital importance to the organism. 
How little the theory of natural selection can be used to 
explain the origin of species will be apparent from the above 
quotation. This is, of course, not an argument against the 
theory itself, which would still be one of vast importance if it 
explained adaptive characters alone; but enough has been 
said, I think, to show that it is improbable that the origin of 
adaptive and non-adaptive characters are to be explained by 
entirely different principles. 
In reply to a criticism of Mivart, Darwin makes the 
further admission as to the insufficiency of the theory of 
natural selection: “When discussing special cases, Mr. 
Mivart passes over the effects of the increased use and 
disuse of parts, which I have always maintained to be highly 
important, and have treated in my ‘ Variation under Domes- 
tication’ at greater length than, as I believe, any other 
writer. He likewise often assumes that I attribute nothing 
to variation, independent of natural selection, whereas in the 
work just referred to I have collected a greater number of 
well-established cases than is to be found in any other work 
known to me.” If this is admitted, and if it can be shown 
